Java is not the same thing as JavaScript (see this article for information about JavaScript).

Before Firefox can run Java applets you must have the Java plugin properly installed and enabled. Starting in Firefox 3.6, Firefox also requires the new Java plugin included in Java 6 Update 10 or above.

This article will help you install or update Java and get it working in Firefox.

Warning: There is a recent and widespread security issue where a malicious website can exploit older Java versions (Version 6 update 29 and earlier, also written as 1.6.0_29) to gain control of your computer. Firefox has blocked these versions for your protection. To fix, simply update Java from the official Java website: http://www.java.com/download

Warning: There is a recent and widespread security issue where a malicious website can exploit older Java versions (Version 6 update 29 and earlier, also written as 1.6.0_29) to gain control of your computer. Firefox has blocked these versions for your protection. At this time, there is no version of Java available from Apple that does not contain this vulnerability.

Testing Java

Java Tester includes links to verify your Java version and whether Java is enabled.

Enabling Java

If Java is not working, make sure that the Java plugin is enabled in the Add-ons window Manager tab:

At the top of the Firefox window, click on the Firefox buttonOn the menu bar, click on the Tools menuAt the top of the Firefox window, click on the Tools menu, and then click Add-ons. The Add-ons Manager tab will open.Click the menu button
and choose Add-ons. The Add-ons Manager tab will open.

Note: You only need to enable the "Java(TM) Platform" plugin, if it is disabled. The "Java Deployment Toolkit" plugin is used by Java developers to detect your Java version and to deploy their Java applications and does not need to be enabled for Java to work.

Other software that may block Java

Even if Java is installed and enabled in Firefox, it may be blocked by other software or Firefox add-ons, such as the following:

The ZoneAlarm Pro software firewall can block Java. For more information on enabling Java through this program, see the ZoneAlarm Pro forum.

The NoScript extension for Firefox will block Java. For more information, see the NoScript FAQ

Installing or updating Java

Manual install or update

Click the Download Now button to download the Java installer to your computer.

After the down is complete, close Firefox.

Open the file you downloaded to start the Java installation.

Automatic update

Java for Windows includes a Java Update feature that, in Windows 2000 and later, periodically checks for updates and notifies you when an update is available for installation.

Note: To eliminate potential security vulnerabilities and to save disk space, you should remove any older Java versions that may still be installed. For more information, visit java.com.

Troubleshooting

After enabling Java in your operating system and through your Firefox options, Java may still fail to work properly. To activate Java, try the following:

Remove outdated Java plugin files from the Firefox plugins folder:

Note: It is recommended that you do not copy Java plugins from other locations to the Firefox plugins folder. Outdated Java plugins can cause Java not to work if you update Java and then uninstall the older Java version, if plugins from the old Java version are still in the Firefox plugins folder.

At the top of the Firefox window, click on the Firefox buttonOn the menu bar, click on the Tools menuAt the top of the Firefox window, click on the Tools menu, and then click Add-ons. The Add-ons Manager tab will open.Click the menu button
and choose Add-ons. The Add-ons Manager tab will open.

In the Add-ons Manager tab, select the Plugins panel.

Select the Java(TM) Platform plugin and make sure that it is enabled.

Check if the Java(TM) Platform plugin is correctly detected. All Java plugins listed in the Add-ons window Manager tab should match the version number of the currently installed Java plugin. For example, if Java 6 Update 24 is currently installed, the Java plugin in the Add-ons window Manager tab should be listed as Java(TM) Platform SE 6 U24.

If you find Java plugin files listed that do not match your current version, that means that the Firefox plugins folder contains outdated Java plugin files which should be removed. This folder is typically in the following location:C:\Program Files\Mozilla Firefox\plugins on 32-bit Windows, C:\Program Files (x86)\Mozilla Firefox\plugins on 64-bit WindowsJava plugin files from older versions in the Firefox plugins folder can prevent Java from working. For more information, see the PluginDoc Java FAQ.

Add missing registry entry: Sometimes a Windows registry entry that Java needs may be missing. To fix, you should re-install Firefox - see the instructions in How to download and install Firefox on Windows for installation instructions.

On Mac OS X 10.6 and below, Java is installed with the operating system. To update Java, use the Mac OS X Software Update feature.

Troubleshooting

For Mac OS X 10.5, Apple's Java Update 10 removed support for Java Plugin2, preventing Firefox and other non-Apple browsers from detecting that Java is installed. Mozilla fixed the problem in Firefox 5.0.1 and above so, in order to run Java applets, you should update to the latest version of Firefox.